The heat was on – along with the power – in the Big Apple yesterday as New Yorkers baked during the second day of a sweltering heat wave and city officials prayed the electricity would hold up.

The mercury hovered in the high 90s for most of the sticky, hazy afternoon, with the brutal humidity making it feel like an oppressive 105 degrees outdoors.

More of the hot stuff is on the way today – temperatures are expected to be in the mid-90s, the National Weather Service said.

And the heat wave isn’t supposed to break until Tuesday, after a storm moves over New York – prompting city officials to urge people to try to keep cool but still save electricity during the third heat wave of the year.

“This is a very, very difficult day,” Mayor Giuliani said. “It’s a day on which people have to be very careful in avoiding strenuous activity and direct exposure to the sun.”

Giuliani and Jerry Hauer, who heads the mayor’s Office of Emergency Management, asked New Yorkers to conserve energy – and to call the heat hot line, (800) 4-COOL-NY, for information about the city’s neighborhood cooling centers.

They also asked residents to check on elderly and ill neighbors as often as possible.

Meanwhile, city officials kept in close contact with Con Ed to monitor trouble spots in the hopes of warding off a repeat of the July 6 blackouts that hit more than 200,000 people in Washington Heights, Inwood and other parts of the city.

The July 4-7 heat wave that caused the blackouts also claimed 31 lives.

Power was back up in Westchester, where the lights went out on 3,000 customers Friday night, Con Ed spokesman Joseph Petta said. At about 1 p.m., only 10 Con Ed customers around the region were without power, he said.